At the age when most Brits graduate from university, Martin Padfield was doing hard labour for the Church of Scientology in the Californian desert. He had to wear a black boiler suit in the baking sun all day, and sleep in a room with “dozens of others” by night, all the while being treated as “the scum of the earth” by the church’s elite at the secretive International Base.

“I didn’t know where I was, I had no contacts in the US outside of Scientology, I had no passport, no money and no possessions. Where was I going to go?”

Padfield wasn’t the son of lifetime Scientologists, nor was he the victim of a violent abduction. He is the son of an RAF officer from the stockbroker belt and the story of his 31-year misery at the hands of one of the world’s most controversial organisations is a tale of extended naivety and delayed but terrible disappointment. The church, best known for its celebrity members who include Tom Cruise, John Travolta and Agyness Deyn’s new actor husband Giovanni Ribisi, is back in the news this autumn as the subject of a new movie, The Master, starring Philip Seymour Hoffman, out in two weeks.

Now living in Crawley with his non-Scientologist wife and two young daughters, having left the church noisily three years ago, the 50-year-old narrates the story with reserve. Before I meet him, he explains that he wasn’t one of the Scientologist apostates who would rant and rave — he just wants rank-and-file Scientologists to know that their movement is “a dangerous, corrupt and sinister cult”, so some of them can escape as he has done.

It all began when Padfield was 19 with a conversation with a Scientologist builder working for his parents at their home in Hinchley Wood, near Esher. The builder “seemed to know things I didn’t”, so Padfield took himself up to the Scientology centre on Tottenham Court Road, bought some books and began his journey. He says he was “utterly impressed” by the answers L Ron Hubbard’s system of self-help and spiritual guidance offered, and still uses some of the practical methods.

In early 1982, in his second term at Loughborough University, he called his father. “‘Daddy, I’ve decided to join Sea Org’ — I remember the call to this day,” he says. “There was a long pause at the other end of the phone line.” Sea Organisation is an elite unit of the most loyal full-time employees of the church of Scientology, who sign billion-year contracts, wear naval uniforms (owing to their founding on three ships in the Sixties) and perform Scientology’s most important work.

Despite his “obvious disappointment”, Padfield senior didn’t object, and even drove his son to the disused convent near Rottingdean, East Sussex, where his son’s training began.

The pay was £10 a week for dawn-to-dusk manual work. “On Saturdays we would get three hours CSP [Clean Ship Programme], which is hygiene time, to do your washing. But basically we had no contact with the outside world. It was always cold,” says Padfield.

It wasn’t until his transfer to California two years later, though, that he understood the isolation and exploitation the church could visit upon its employees. The International Base at Gilman Hot Springs, near Hemet, was Scientology’s most notorious facility. “We arrived in a minibus, in the middle of the night. I don’t think that was accidental. I knew I was somewhere in California, and that’s it.”

Even as a Sea Org member, the life at Hemet was “a culture shock”. “There was no light-heartedness, there was little laughter or joviality. It was intense and threatening — there was always the sense of fear and anxiety — and production targets were ruthless and had to be met.”

Padfield worked on the base’s elaborate security apparatus, which consisted of motion sensors, barbed-wire fences and a lookout tower overlooking the entire complex called the Eagle’s Nest. When he dozed off for a few minutes on a night shift, and received a letter from his mother quoting an article criticising the church soon afterwards, he was thrown into the feared Rehabilitation Project Force, which is where the boiler suits and spirit-sapping labour began.

“In practice it is little more than a punishment regime, and some have been on it for years, even decades,” Padfield says. “The schedule is even more gruelling, the targets even more insane, and the punishments for slacking or missing targets could be brutal.”

What Padfield hated most about his nine months in the RPF was the stigma of being “the lowest of the low”. He says RPF members working at Int had to defer to any new recruits joining the base. “You were the scum of the earth.”

An expired visa gave Padfield his reprieve at the age of 23 but he was to spend the next few troubled decades moving in and out of full-time Scientology. A fling with a fellow Sea Org member saw him thrown out of the order (no sex before marriage at Sea Org), yet he undertook several trips back to America as an active Scientologist for auditing, counselling and hour upon hour of highly personal “security checks”.

Padfield’s final departure in 2009 lost him most of his Scientologist friends, who adhered to the church’s policy of “disconnection” with those who leave the flock. His 10-year-old daughter cries herself to sleep to this day after losing her closest playmate through a disconnection. “I’ve sent countless texts and voicemails pleading with them but they don’t reply to anything,” Padfield says. He still has debts remaining from the nearly £100,000 he spent on courses, donations and materials during his time with the church, and is suspicious of one friend who still maintains contact.

Tomorrow he will join a handful of ex-members of the church in East Grinstead to tell his story at an event called “The cult in your backyard”, timed to coincide with Scientology’s annual convention down the road. He wants to show his old friends “what’s behind the curtain”. And to 19-year-olds from suburbia with questions to ask, it’s a warning served.

When approached by the London Evening Standard, the Church of Scientology replied:

“Mr Padfield is a member of a small group of apostates who are anti-Scientologists that seek to spread false information. We know Mr Padfield was removed from Church staff in the early 1990s and has no knowledge of the Church today whatsoever.”